1. Field of the Invention
This invention relates to an optical card on which information can be recorded, and an apparatus for recording information on and/or reproducing information from the optical card.
2. Description of the Prior Art
An optical card has advantages over other memory devices in that it has a large memory capacity despite its small size, and is easily carried. Thus optical cards are widely used in various information processing fields. Such optical cards include the read only type and the so-called write once type. In an optical card of the read only type, information is recorded during manufacturing prohibiting the additional recording of information on the card. By contrast, in an optical card of the write once type, information can be recorded once by the holder of the card. An optical card of the write once type will be described below to illustrate the prior art in contrast to the present invention.
A typical example of optical cards is shown in FIG. 5. The optical card 50 of FIG. 5 has a plate-like body 51, and a rectangular memory region 52 made of a magnetooptical material on which information can be optically recorded. FIG. 6 shows the structure of the memory region 52 in more detail. In the memory region 52, a plurality of guide tracks 61 are disposed in a parallel manner at fixed intervals. The guide tracks 61 are used in controlling an optical head of a recording and reproducing apparatus for the card which will be described below. Along each of the guide tracks 61, a pit train 62 is formed having a stripe portion (record track) 63 of fixed width between the guide track 61 and the pit train 62. Each pit train 62 consists of a plurality of circular pits 62a arranged in a row. Information is recorded as dot patterns 64 formed in the record tracks 63. The pit train 62 is used for obtaining synchronizing signals.
A recording and reproducing apparatus for the optical card 50 is shown in FIG. 4. When information is recorded on or reproduced from the optical card 50, the optical card 50 is inserted through a slot (not shown) of the apparatus of FIG. 4, and then immovably rests on a carrying means (not shown) which, as shown by bidirectional arrow A, is moved reciprocally by a card-carrying motor 41. An optical head 42 is movably disposed above the moving path of the optical card 50. As shown by bidirectional arrow B, the optical head 42 is reciprocally moved by a motor 43 in a direction perpendicular to the moving direction of the card 50.
When information is recorded on or reproduced from the card 50, the optical head 42 is moved so that it is positioned above the stripe portion 63 in which information is to be recorded or from which information is to be reproduced. While changing the relative positional relation between the optical card 50 and the optical head 42, a tracking signal is obtained from the guide track 61, and the synchronizing signal from the pit train 62. The fine adjustment of the light beam of the optical head 42 is conducted on the basis of the obtained tracking signal. The recording and reproduction of information is performed in accordance with the synchronizing signal.
In the prior art optical card 50, the guide track 61 and the pit train 62 must be formed for each record track 63. Namely, the memory region 52 contains the portions 61 and 62 which are useless in the storage of information, resulting in the prior art optical card having a reduced capacity for storing information.